Overbanking preventive means for a balance wheel



Jan. 23, 1962 F. KOEHLER 3,017,741

- OVERBANKING PREVENTIVE MEANS FOR A BALANCE WHEEL Filed March 17, 1959 INVENTOR F red Koeh/er ATTORNEYS United States Patent 3,017,741 OVERBANKING PREVENTIVE MEANS FOR A BALANCE WHEEL Fred Koehler, Lancaster, Pa., assignor to Hamilton Watch Company, Lancaster, Pa., a corporation of Pennsylvania Filed Mar. 17, 1959, Ser. No. 799,952 3 Claims. (Cl. 58-107) This invention relates to an overbanking control means and in particular relates to an overbanking control for an electromagnetically driven watch.

In conventional watches of the type driven by a mainspring, overbanking or an excessive angular oscillation of the balance wheel is prevented by the engagement of a jewel pin with a pallet fork, but in a watch of the electromagnetic type, there is no pallet fork and no jewel pin, so that should the balance wheel oscillate through an arc in excess of 360, the contact mechanism will be actuated a second time during the same oscillation result ing in an additional impulse to the wheel. This overswinging is generally brought about by a shock or sudden movement of the person wearing the watch, and some means for preventing the balance wheel from turning through an angle of rotation in excess of 360 in a single direction per oscillation must be provided.

One such balance wheel control device is disclosed in assignees Patent No. 2,717,487 which issued on September 13, 1955. In this patent a pin is carried by a crossarm of the balance wheel which is positioned in close proximity to the hairspring so that as the hairspring attempts to expand beyond a pre-set radius it engages the pin and is restrained thereby.

While the foregoing balance wheel control device has proven to be most satisfactory, I have now discovered that it is possible to provide an overbanking control which need not be limited to an embodiment in which the balance wheel and the hairspring are in very close proximity. Moreover, I have found that by using the same collet which carries the hairspring to carry an overbanking control member, that the shape of the balance wheel need not be limited to one having a crossarm or other structure suitable for attaching the overbanking control means. That is to say, the overbanking control of the present invention may be completely dissociated from the balance wheel both in regard to the proximity of the hairspring to the balance wheel and with respect to the structure of the balance wheel.

According to the present invention, the overbanking control is preferably made flexible so as to permit the overbanking control member to flex out of the Way of the hairspring when an unusual shock or jolt is encountered. Additionally, I have now devised an overbanking control for an electric wrist watch which may be adjusted so as to permit variations in the allowable expansion of the hairspring before the overbanking control begins to function. All this has been provided in a structure which is simple in nature, inexpensive to produce and extremely smooth in performance.

It is accordingly a primary object of the invention to provide an overbanking control for an electromagnetically driven wrist watch which is not dependent upon the balance wheel being in close proximity to the hairspring.

It is another object of the present invention to provide an overbanking control for an electromagnetically driven wrist watch which permits an alteration of the drive position of the balance wheel without effecting the overbanking control.

It is another object of the present invention to provide an overbanking control which is flexible so as to yield 3,017,741 Patented Jan. 23, 1962 to the hairspring when a shock or jolt of predetermined magnitude is imparted to the watch.

It is still another object of the invention to provide an overbanking control for an electromagnetically driven wrist watch in which means are provided to vary the permissible expansion of the hairspring before the overbanking control becomes effective.

It is still a further object of the invention to provide an overbanking control which is extremely simple, inexpensive to manufacture and smooth in action.

These and further objects and advantages of the present invention shall become more apparent upon reference to the following specification and claims and appended drawings wherein:

FIGURE 1 is a front view partially in section showing the overbanking control means of the present invention; and

FIGURE 2 is a sectional view taken along the lines 22 of FIGURE 1 with portions of the hairspring removed.

Referring both to FIGURES 1 and 2 of the drawing, there is shown a balance staff 10 which is supported and oscillated in customary fashion for an electric wrist watch. A collet 12 frictionally engages balance staif 10 and is .provided with a slot 14 to permit the friction between the two members to be adjusted. A hairspring indicated generally at 16 has its innermost coil 18 received within a slot 20. The slot 20 is cut so as to form a chord of a circle in collet 12. The structure described thus far is standard in the watch making art.

An overbank control member of the present invention is indicated generally at 22 and is frictionally received within a slot 24 in collet 12. The overbank control member 22 consists of an elongated stem 26 which extends radially outwardly from slot 24 substantially parallel to the plane of hairspring 16 and a V-shaped end 28 integral with the free end of the elongated stem 26.

It will be noted that the apex of the V-shaped end 28 of the overbank control member 22 extends upwardly in FIGURE 1 so that the V-shaped end 28 is engageable with the outermost coil 30 of hairspring 16 when the hairspring is in its extended position shown in phantom. The rest or neutral position for hairspring 16 is shown by the solid lines. It is also to be noted that the end of the elongated stem is spaced from the balance staff within slot 24 so as to permit axial adjustment of the overbank control member 22. By virtue of the length of the overbank control member 22 in comparison to its cross sectional dimension, overbank control member 22 is slightly flexible thereby permitting the V-shaped end 28 to yield to hairspring 16 when a predetermined force is exerted on the V-shaped end 28 by the hairspring 16 such as may be caused by an unusual shock or jolt,

A counterweight 32 is frictionally received within slot 34 and positioned diametrically opposite the overbank control member 22 so as to counterbalance this member.

Although a substantial portion of the operation of the overbank control means will be apparent from the foregoing description, a brief summary of the operation is as follows.

Oscillations imparted to the balance staff 10 cause hairspring 16 to expand and contract from its rest position shown in solid lines. The overbank control member 22 is manually positioned in slot 24 and frictionally held thereby so as to become operative at a desired number of degrees of oscillation for the balance staff 10 which is a function of the expansion and contraction of hairspring 16. counterweight 32 is similarly positioned within slot 34 so as to counterbalance the weight of the overbank control member 22.

If the magnitude of oscillation imparted to balance staff is as great as the pre-selected value for the overbanking control means to become operative, the outermost coil 30 of hairspring 16 engages the V-shaped end 28 of the overbank control member 22 which exerts a restraining force on the hairspring 16 to bring the oscillating balance staff to a slow stop. The resiliency of the overbank control member 22 is made such as to permit the V-shaped end 28 to yield when a force of sufficient predetermined magnitude is imparted through the hairspring 16 to the V-shaped end 28. Excessive bending of the hairspring 16 is thereby minimized, thus lessening the chances of fracture for the hairspring.

It will be apparent from the foregoing description that an overbanking control means has been provided for an electromagnetically driven wrist watch which is completely independent of the balance wheel both in regard to the proximity of the balance wheel to the hairspring and the capability of the balance wheel to support an overbanking control means. Since the overbanking control means is completely independent of this balance wheel, it permitsan alteration of the drive position for the balance Wheel without affecting the overbanking control. Also, it is possible to utilize an overbanking control which is itself flexible to enable it to yield to the hairspring thereby preventing fracture of the hairspring. The overbanking control means possesses additional advantages in that it is adjustable, simple in construction, inexpensive and possesses smooth operating characteristics.

The invention may be embodied in other specific forms Without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

What is claimed and desired to be secured by United States Letters Patent is:

1. In a watch of the electromagnetic type having an oscillatable balance stafr driven by a source of motive power, a collet frictionally mounted on said balance staff, a hairspring carried by said collet, said collet havbalance staff driven by a source of motive power, a hair spring having one end fixed relative to said staif, an elongated motion-limiting member rigidly supported at one end by said staff and having means carried at its free end engageable with the outer coil of said hairspring to prevent overbanking of said timepiece, said motion-limiting member being flexible whereby said member is able to yield in a direction parallel with the axis of said balance stafl? in response to a predetermined force applied to it by the outer coil of said hairspring.

3. An electric timepiece comprising an oscillatable balance staff driven by a source of motive power, a collet frictionally mounted on said balance staff, a hairspring carried by said collet, and elongated motion-limiting member attached at one end to said collet, a V-shaped member carried at the free end of said elongated motionlirniting member engageable with the outer coil of said hairspring to prevent overbanking of said watch, said elongated motion-limiting member being flexible whereby said member is able to yield in a direction parallel with the axis of said balance staff in response to a predetermined force exerted on it by the outer coil of said hairspring.

References Cited in the file of this patent UNITED STATES PATENTS 2,601,174 Smith July 17, 1952 2,717,487 Koehler Sept. 13, 1955 FOREIGN PATENTS 91,358 Germany Aug. 6, 1896 

